Method of operating a vehicle and a vehicle

ABSTRACT

A method of operating a vehicle at different altitudes. The vehicle has an engine, a throttle valve and a throttle operator. A continuously variable transmission has a driving pulley connected to the engine, a driven pulley, and a belt operatively connecting therebetween. A ground engaging member is operatively connected to the driven pulley. A piston is connected to the driving pulley. A control unit controls actuation of the piston and the piston force. The method includes determining an altitude and/or an atmospheric pressure, a driven pulley speed, and at least one of the throttle operator position and the throttle valve position. The piston is selectively actuated based on the altitude and/or the atmospheric pressure. The piston force is controlled based on the driven pulley speed, and at least one of: the throttle operator position and the throttle valve position. Vehicles and other methods of operation thereof are also disclosed.

CROSS-REFERENCE

The present application claims priority to U.S. Provisional PatentApplication No. 61/934,498, filed on Jan. 31, 2014, the entirety ofwhich is incorporated herein by reference.

The present application is related to International Patent ApplicationNo. PCT/US2013/062125 filed on Sep. 27, 2013, U.S. Provisional PatentApplication No. 61/758,322 filed Jan. 30, 2013, and U.S. ProvisionalPatent Application No. 61/768,285 filed on Feb. 22, 2013, the entiretyof all of which is incorporated herein by reference.

TECHNICAL FIELD

The present technology relates generally to a continuously variabletransmission and to vehicle control methods.

BACKGROUND

Endless belt type continuously variable transmissions (CVT) are used inmany types of vehicles such as snowmobiles, all terrain vehicles (ATVs),scooters and the like to obtain an infinite number of gear ratiosbetween the engine and the vehicle's wheels. Typically, the CVTs aremechanically controlled by means of centrifugal weights (usually on thedriving side) acting against the force of a spring to provide thedesired gear ratios. CVT characteristics, including variation of thegear ratio as a function of engine speed, vehicle speed, torque and thelike, can be tailored by appropriate choice of flyweights and spring onthe driving side, and the cams on the driven side.

Mechanically controlled CVTs have limited control options as theconfiguration of the different components cannot be changed on-the-flybased on operating conditions. Mechanically controlled CVTs can havepoor power efficiency due to frictional losses arising from the beltedconstruction. Furthermore, when driving at constant high speeds, theengine, and other related elements inside the engine, operating at highrotational speeds (RPM) cause undesirable noise and vibrations, as wellas high fuel consumption.

In some CVTs, especially in stationary applications, the mechanicalcontrols have been replaced by a pneumatic or hydraulic system forchanging the CVT gear ratio. Such fully controlled CVTs, where one orboth of the pulleys is controlled, whether hydraulically, pneumaticallyor electrically, require the attachment of additional components to theCVT, such as pumps and reservoirs, adding to its weight and cost.Furthermore, in such systems any loss of CVT control could result in thevehicle becoming inoperable.

There is thus a need for a method of controlling a CVT which allows forfast and efficient adjustments of its configuration based on vehicleoperating conditions.

SUMMARY

It is an object of the present technology to ameliorate at least some ofthe inconveniences present in the prior art.

According to one aspect of the present technology, there is provided amethod of operating a vehicle at different altitudes. The vehicleincludes an engine, a throttle operator being operable by a driver ofthe vehicle, a throttle valve regulating airflow to the engine, athrottle valve position of the throttle valve being based at least inpart on a throttle operator position of the throttle operator, and acontinuously variable transmission (CVT) operatively connected to theengine. The CVT includes a driving pulley, a driven pulley, and a beltoperatively connecting the driving pulley to the driven pulley. At leastone ground engaging member operatively connects to the driven pulley andincludes at least one of: a wheel and a track. A piston is operativelyconnected to the driving pulley for applying a piston force to thedriving pulley when actuated, and thereby changing an effective diameterof the driving pulley. A control unit controls actuation of the pistonand the piston force. The method includes determining at least one of analtitude and an atmospheric pressure, determining a driven pulley speed,and determining at least one of the throttle operator position and thethrottle valve position. The piston is selectively actuated based on theat least one of the altitude and the atmospheric pressure. The pistonforce is controlled based on the driven pulley speed and the at leastone of the throttle operator position and the throttle valve position.

In some implementations, the piston force is controlled based on acontrol map.

In some implementations, the control map includes a first control mapcorresponding to a first altitude, and a second control mapcorresponding to a second altitude.

In some implementations, the one of the altitude and the atmosphericpressure is the altitude. The piston force is set to be zero responsiveto the determined altitude being greater than a high altitude threshold.

In some implementations, the vehicle further comprises a mode switch forselecting one of a plurality of modes of operation of the vehicle. Themethod further includes determining the one of the plurality of modes ofoperation that has been selected, and controlling the piston force basedat least in part on the selected one of the plurality of modes ofoperation of the vehicle.

In some implementations, the piston force is controlled based on acontrol map associated with the selected one of the plurality of modesof operation of the vehicle.

In some implementations, an engine speed is determined, the piston forceis set to be at least as great as a minimum piston force, the minimumpiston force being predefined based on the determined engine speed.

In some implementations, the vehicle further comprises a plurality ofcentrifugal weights operatively connected to the driving pulley forcontrolling the effective driving pulley diameter. The method furtherincludes controlling the effective diameter of the driving pulley, viathe centrifugal weights, responsive to a driving pulley speed.

In some implementations, the piston is at least one of pneumaticallyactuated and hydraulically actuated.

According to another aspect of the present technology, there is provideda method of operating a vehicle. The vehicle includes an engine, athrottle operator being operable by a driver of the vehicle, a throttlevalve regulating airflow to the engine, a throttle valve position of thethrottle valve being based at least in part on a throttle operatorposition of the throttle operator, and a continuously variabletransmission (CVT) operatively connected to the engine. The CVT includesa driving pulley, a driven pulley, and a belt operatively connecting thedriving pulley to the driven pulley. At least one ground engaging memberoperatively connects to the driven pulley and includes at least one of:a wheel and a track. A piston is operatively connected to the drivingpulley for applying a piston force to the driving pulley when actuated,and thereby changing an effective diameter of the driving pulley. Acontrol unit controls actuation of the piston and the piston force. Themethod includes determining at least one of the throttle operatorposition and the throttle valve position, detecting a parking/drive awaycondition indicative of one of a parking operation and a drive-awayoperation of the vehicle, and responsive to the detection of theparking/drive away condition, actuating the piston and controlling thepiston force based on the at least one of the throttle operator positionand the throttle valve position.

In some implementations, the parking/drive away condition includes avehicle speed being lower than a parking threshold vehicle speed, and anengine speed being lower than a parking threshold engine speed. Themethod further includes determining an engine speed, and determining avehicle speed.

In some implementations, the parking threshold vehicle speed is 10 km/h.

In some implementations, the parking threshold driven pulley speed is1500 rpm.

In some implementations, the vehicle further includes a brakeoperatively connected to the ground engaging member, and theparking/drive away condition further includes the brake beingunactuated.

In some implementations, the vehicle further comprises an engine coolanttemperature sensor sensing an engine coolant temperature. The methodfurther includes determining the engine coolant temperature, andcontrolling the piston force based on the engine coolant temperature.

In some implementations, the piston force is a first piston force whenthe engine coolant temperature is a first engine coolant temperature,the first engine coolant temperature being lower than a threshold enginecoolant operating temperature. The piston force is a second piston forcewhen the engine coolant temperature is a second engine coolanttemperature. The second engine coolant temperature is higher than thethreshold engine coolant operating temperature. The second piston forceis lower than the first piston force.

In some implementations, the piston force is controlled independently ofan engine speed when the parking/drive away condition is detected.

In some implementations, the piston force is controlled independently ofa driven pulley speed when the parking/drive away condition is detected.

In some implementations, the vehicle further comprises a mode switch forselecting one of a plurality of modes of operation of the vehicle. Themethod further includes determining the one of the plurality of modes ofoperation that has been selected, and controlling the piston force basedat least in part on the selected one of the plurality of modes ofoperation of the vehicle.

In some implementations, an engine speed is determined and the pistonforce is set to be at least as great as a minimum piston force, theminimum piston force being predefined based on the determined enginespeed.

In some implementations, the piston is at least one of pneumaticallyactuated and hydraulically actuated.

According to another aspect of the present technology, there is provideda method of operating a vehicle. The vehicle includes an engine, athrottle operator being operable by a driver of the vehicle, a throttlevalve regulating airflow to the engine, a throttle valve position of thethrottle valve being based at least in part on a throttle operatorposition of the throttle operator, and a continuously variabletransmission (CVT) operatively connected to the engine. The CVT includesa driving pulley, a driven pulley, and a belt operatively connecting thedriving pulley to the driven pulley. At least one ground engaging memberoperatively connects to the driven pulley and includes at least one of:a wheel and a track. A piston is operatively connected to the drivingpulley for applying a piston force to the driving pulley when actuated,and thereby changing an effective diameter of the driving pulley. Acontrol unit controls actuation of the piston and the piston force. Themethod includes determining an engine speed and controlling the pistonforce based on the engine speed.

In some implementations, the piston force is set to be at least as greatas a minimum piston force, the minimum piston force being predefinedbased on the determined engine speed.

In some implementations, at least one of the throttle operator positionand the throttle valve position is determined, and a negative loadcondition indicative of a negative load on the engine is detected.Responsive to the detection of the negative load condition, the pistonforce is controlled based on an engine speed. The negative loadcondition includes the engine speed being greater than a downhillthreshold engine speed, and at least one of the throttle operationposition being lower than a downhill threshold throttle operationposition, and the throttle valve position being lower than a downhillthreshold throttle valve position.

In some implementations, the piston force is controlled independently ofthe throttle valve position and the throttle operator position when thenegative load condition is detected.

In some implementations, the piston force is controlled independently ofa driven pulley speed when the negative load condition is detected.

In some implementations, the vehicle further includes an engine coolanttemperature sensor sensing a temperature of an engine coolant. Themethod further includes determining the engine coolant temperature, andcontrolling the piston force based on the engine coolant temperature.

In some implementations, the piston force is a first piston force whenthe engine coolant temperature is a first engine coolant temperature anda second piston force when the engine coolant temperature is a secondengine coolant temperature. The first engine coolant temperature islower than a threshold engine coolant operating temperature. The secondengine coolant temperature is higher than the threshold engine coolantoperating temperature. The second piston force is lower than the firstpiston force.

In some implementations, the vehicle further comprises a mode switch forselecting one of a plurality of modes of operation of the vehicle. Themethod further includes determining the one of the plurality of modes ofoperation that has been selected, and controlling the piston force basedat least in part on the selected one of the plurality of modes ofoperation of the vehicle.

In some implementations, the piston is at least one of pneumaticallyactuated and hydraulically actuated.

According to yet another aspect of the present technology, there isprovided a method of operating a vehicle. The vehicle includes anengine, a throttle operator being operable by a driver of the vehicle, athrottle valve regulating airflow to the engine, a throttle valveposition of the throttle valve being based at least in part on athrottle operator position of the throttle operator, and a continuouslyvariable transmission (CVT) operatively connected to the engine. The CVTincludes a driving pulley, a driven pulley, and a belt operativelyconnecting the driving pulley to the driven pulley. At least one groundengaging member operatively connects to the driven pulley and includesat least one of: a wheel and a track. A piston is operatively connectedto the driving pulley for applying a piston force to the driving pulleywhen actuated, and thereby changing an effective diameter of the drivingpulley. A control unit controls actuation of the piston and the pistonforce. The method includes detecting a stall condition indicative of thevehicle being stalled, and responsive to the detection of the stallcondition, setting the piston force to be zero.

In some implementations, method includes determining a driven pulleyspeed. The stall condition includes a driven pulley speed of the drivenpulley decreasing, and a rate of decrease of the driven pulley speedbeing greater in magnitude than a stall threshold rate.

In some implementations, the stall threshold rate is 150 rpm/s2.

In some implementations, the vehicle has a brake operatively connectedto the at least one ground engaging member, and the stall conditionfurther includes the brake being actuated.

In some implementations, the piston is at least one of pneumaticallyactuated and hydraulically actuated.

According to yet another aspect of the present technology, there isprovided a method of operating a vehicle. The vehicle includes anengine, a throttle operator being operable by a driver of the vehicle, athrottle valve regulating airflow to the engine, a throttle valveposition of the throttle valve being based at least in part on athrottle operator position of the throttle operator, and a continuouslyvariable transmission (CVT) operatively connected to the engine. The CVTincludes a driving pulley, a driven pulley, and a belt operativelyconnecting the driving pulley to the driven pulley. At least one groundengaging member operatively connects to the driven pulley and includesat least one of: a wheel and a track. A piston is operatively connectedto the driving pulley for applying a piston force to the driving pulleywhen actuated, and thereby changing an effective diameter of the drivingpulley. A control unit controls actuation of the piston and the pistonforce. The method includes determining a driven pulley speed of thedriven pulley. An uphill stand condition indicative of the vehicle beingstopped on an uphill is detected and responsive to the detection of theuphill stand condition, the piston force is controlled based on thedriven pulley speed.

In some implementations, the vehicle further includes a brakeoperatively connected to the at least one ground engaging member. Theuphill stand condition includes an actuation of the brake followed by adeactuation of the brake, and at least one of the throttle operatorposition being lower than an uphill stand throttle operator thresholdand the throttle valve position being lower than an uphill standthrottle valve threshold.

In some implementations, an inclination of the ground is sensed and theuphill stand condition further includes the sensed inclination beinguphill.

In some implementations, controlling the piston force includes,responsive to the driven pulley speed being negative, increasing thepiston force until at least one of the following occurs: the drivenpulley speed becomes zero, and the piston force becomes equal to amaximum piston force.

In some implementations, the piston force is increased at a rate suchthat the piston force increases to the maximum piston force within anuphill stand threshold time period.

In some implementations, the uphill stand threshold time period is onesecond.

In some implementations, the piston is at least one of pneumaticallyactuated and hydraulically actuated.

In some implementations, an engine speed is determined and the pistonforce is set to be at least as great as a minimum piston force, theminimum piston force being predefined based on the determined enginespeed.

According to another aspect of the present technology, there is provideda vehicle having an engine, a throttle operator being operable by adriver of the vehicle, a throttle valve regulating airflow to theengine, a throttle valve position of the throttle valve being based atleast in part on a throttle operator position of the throttle operator,and a continuously variable transmission (CVT) operatively connected tothe engine. The CVT includes a driving pulley, a driven pulley, and abelt operatively connecting the driving pulley to the driven pulley. Atleast one ground engaging member operatively connects to the drivenpulley and includes at least one of: a wheel and a track. A piston isoperatively connected to the driving pulley for applying a piston forceto the driving pulley when actuated, and thereby changing an effectivediameter of the driving pulley. A control unit controls actuation of thepiston and the piston force. An altitude sensor senses at least one ofan altitude and an atmospheric pressure. The control unit is configuredto control actuation of the piston and the piston force based on thesensed at least one of the altitude and the atmospheric pressure beingsensed.

In some implementations, a plurality of centrifugal weights isoperatively connected to the driving pulley for controlling an effectivediameter thereof.

In some implementations, the vehicle further includes a mode switch forselecting one of a plurality of modes of operation of the vehicle, thecontrol unit being configured to control the piston force based at leastin part on the selected one of the plurality of modes of operation ofthe vehicle.

In some implementations, the vehicle further includes at least one of ahydraulic system and a pneumatic system connected to the piston, thecontrol unit being connected to the at least one of the hydraulic systemand the pneumatic system for controlling the piston force.

According to another aspect of the present technology, there is provideda vehicle having an engine, a throttle operator being operable by adriver of the vehicle, a throttle valve regulating airflow to theengine, a throttle valve position of the throttle valve being based atleast in part on a throttle operator position of the throttle operator,and a continuously variable transmission (CVT) operatively connected tothe engine. The CVT includes a driving pulley, a driven pulley, and abelt operatively connecting the driving pulley to the driven pulley. Atleast one ground engaging member operatively connects to the drivenpulley and includes at least one of: a wheel and a track. A piston isoperatively connected to the driving pulley for applying a piston forceto the driving pulley when actuated, and thereby changing an effectivediameter of the driving pulley. A control unit controls actuation of thepiston and the piston force. An engine coolant temperature sensor sensesan engine coolant temperature of an engine coolant system of the engine.An engine speed sensor senses an engine speed of the engine. A drivenpulley speed sensor senses a driven pulley speed of the driven pulley.The control unit is configured to control actuation of piston and thepiston force based on at least one of: the selected one of the pluralityof modes of operation of the vehicle, the sensed engine coolanttemperature, the sensed engine speed, and the sensed driven pulleyspeed.

In some implementations, a plurality of centrifugal weights isoperatively connected to the driving pulley for controlling an effectivediameter thereof.

In some implementations, the vehicle further includes at least one of ahydraulic system and a pneumatic system connected to the piston, thecontrol unit being connected to the at least one of the hydraulic systemand the pneumatic system for controlling the piston force.

In some implementations, the vehicle further comprises a piston forceselector operable by the driver of the vehicle. The control unit isconnected to the piston force selector for receiving a driver selectiontherefrom and configured to control the piston force based at least inpart on the received driver selection.

In another aspect, the method includes controlling the piston forcebased at least in part on the mode of operation of the vehicle.

For purposes of the present application, terms related to spatialorientation when referring to a vehicle and components in relation tothe vehicle, such as “forwardly”, “rearwardly”, “left”, “right”, “above”and “below”, are as they would be understood by a driver of a vehicle,with the vehicle in a straight ahead orientation (i.e. not steered leftor right), and in an upright position (i.e. not tilted).

Definitions of terms provided herein take precedence over definitionsprovided in any of the documents incorporated herein by reference.

Implementations of the present technology each have at least one of theabove-mentioned object and/or aspects, but do not necessarily have allof them. It should be understood that some aspects of the presenttechnology that have resulted from attempting to attain theabove-mentioned object may not satisfy this object and/or may satisfyother objects not specifically recited herein.

Additional and/or alternative features, aspects, and advantages ofimplementations of the present technology will become apparent from thefollowing description, the accompanying drawings, and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present technology, as well as otheraspects and further features thereof, reference is made to the followingdescription which is to be used in conjunction with the accompanyingdrawings, where:

FIG. 1 is a right side elevation view of a snowmobile;

FIG. 2A is a perspective view, taken from a front, left side, of apowertrain of the snowmobile of FIG. 1;

FIG. 2B is a schematic illustration of a throttle control system of thesnowmobile of FIG. 1;

FIG. 2C is an illustration of the response of a throttle valve to aposition of a throttle operator in different modes of operation of thesnowmobile of FIG. 1;

FIG. 3 is a schematic illustration of elements of an engine control unitof the snowmobile of FIG. 1;

FIG. 4A is a cross-sectional view of a driving pulley of a continuouslyvariable transmission (CVT) of the powertrain of FIG. 2, with thedriving pulley in an inactive configuration;

FIG. 4B is a cross-sectional view of the driving pulley of FIG. 4A in anactive configuration;

FIG. 5 is schematic illustration of a pneumatic control system for theCVT of the powertrain of FIG. 2;

FIG. 6 is a logic diagram illustrating a method of controlling the CVTat different altitudes and in different modes;

FIG. 7 is illustrates a piston force control map for operation in thesport mode at sea level;

FIG. 8A illustrates a piston force control map for operation in thestandard mode at high altitude;

FIG. 8B illustrates a piston force control map for operation in thestandard mode at sea level;

FIG. 9A illustrates a piston force control map for operation in theeconomy mode and at high altitude;

FIG. 9B illustrates a piston force control map for operation in theeconomy mode at sea level;

FIG. 10 illustrates a parking/drive-away piston force control map forthe standard and economy modes showing the piston force as a function ofthrottle operator position and engine temperature;

FIG. 11A illustrates a downhill-minimum force piston force control mapfor operation in the standard mode; and

FIG. 11B illustrates a downhill-minimum force piston force control mapfor operation in the economy mode.

DETAILED DESCRIPTION

The present technology will be described with respect to a snowmobile.However, it is contemplated that the technology could be used in othervehicles, such as, but not limited to, a motorcycle, a three-wheelvehicle and an all-terrain vehicle (ATV). Aspects of the technologycould also be applied to motorized devices, other than vehicles, thatuse a continuously variable transmission (CVT).

Turning now to FIG. 1, a snowmobile 10 includes a forward end 12 and arearward end 14 which are defined consistently with a forward traveldirection. The snowmobile 10 has a frame 16 that includes a tunnel 18,an engine cradle portion 20 and a front suspension assembly portion 22.The tunnel 18, generally formed of sheet metal bent in an invertedU-shape, extends rearwardly along the longitudinal axis 61 of thesnowmobile 10 and is connected at the front to the engine cradle portion20. An engine 24, shown schematically in FIG. 1, is carried by theengine cradle portion 20 of the frame 16. A fuel tank 25, supportedabove the tunnel 18, supplies fuel to the engine 24 for its operation.

Two skis 26 are positioned at the forward end 12 of the snowmobile 10and are attached to the frame 16 through a front suspension assembly 28.The front suspension assembly 28 includes ski legs 30, supporting arms32 and ball joints (not shown) for operatively connecting the respectiveskis 26 to a steering column 34.

An endless drive track 65 is positioned at the rear end 14 of thesnowmobile 10. The drive track 65 is disposed generally under the tunnel18, and is operatively connected to the engine 24 through a continuouslyvariable transmission (CVT) 40 (illustrated schematically by brokenlines in FIG. 1) and a drive sprocket (not shown). The operation of theengine 24 and the CVT 40 will be described in greater detail below. Theendless drive track 65 is driven to run about a rear suspension assembly42 for propulsion of the snowmobile 10.

The rear suspension assembly 42 includes a pair of slide rails 44 insliding contact with the endless drive track 65. The rear suspensionassembly 42 also includes one or more shock absorbers 46 and suspensionarms 48 and 50 to attach the slide rails 44 to the frame 16. One or moreidler wheels 52 are also provided in the rear suspension assembly 42.

At the front end 12 of the snowmobile 10, fairings 54 enclose the engine24 and the CVT 40, thereby providing an external shell that protects theengine 24 and the CVT 40. The fairings 54 include a hood and one or moreside panels which can be opened to allow access to the engine 24 and theCVT 40 when this is required, for example, for inspection or maintenanceof the engine 24 and/or the CVT 40. A windshield 56, connected to thefairings 54 near the front end 12 of the snowmobile 10, acts as awindscreen to lessen the force of the air on the driver while thesnowmobile 10 is moving.

A straddle-type seat 58 is positioned atop the fuel tank 25 and extendsrearward from the fairings 54 to accommodate a driver of the snowmobile10. A rear portion of the seat 58 may include a storage compartment orcan be used to accommodate a passenger seat (not indicated). A footrest60 is positioned on each side of the snowmobile 10 below the seat 58 toaccommodate the driver's feet.

The upper end of the steering column 34 is attached to a steering devicesuch as a handlebar 36 which is positioned forward of the seat 58. Thehandlebar 36 is used to rotate the ski legs 30 and thus the skis 26, inorder to steer the vehicle 10.

A throttle operator 37 in the form of a finger-actuated throttle lever37 is mounted near the left side grip of the handlebar 36. Other typesof throttle operators, such as a thumb-actuated throttle lever and atwist grip, are also contemplated. The throttle lever 37 is normallybiased, typically by a spring, towards a position furthest away from thehandlebar 36. This position of the throttle lever 37 is indicative of adesire for an idle operation of the engine 24 as will be describedbelow. The throttle lever 37 can be pressed towards the handlebar 36 toincrease air flow into the engine 24, and to thereby increase the outputpower of the engine 24 by means of a drive-by-wire (DBW) system. U.S.Provisional Patent Application No. 61/666,443, filed on Jun. 29, 2012,the entirety of which is incorporated herein by reference, providesadditional details of drive-by-wire throttle systems in vehicles. Athrottle operator position PP is defined as a fraction of its fullyactivated position and thus varies between 0% (unactivated or idleposition) and 100% (fully activated when throttle lever 37 is at itsclosest position to the handlebar 36). It is contemplated that thesnowmobile 10 could not have a DBW system.

A brake operator 38 in the form of a finger-actuated brake lever 38 ismounted near the right side grip of the handlebar 36. The brake lever 38is connected to a brake disc (not shown) connected to the sprocket inorder to brake the sprocket, and thereby the endless track 65 in amanner that will be understood by a worker skilled in the art.

A display cluster 64 (FIG. 3) is provided in front of the handlebars 36to display information, such as the vehicle speed, engine speed, vehiclemode, temperature and the like, to the driver of the snowmobile 10. Thedisplay cluster 64 possibly includes one or more gauges, displayscreens, indicator lights and sound output devices such as speakers,alarms and the like.

A mode switch 62 (FIG. 3) is provided near or on the handlebar 62. Themode switch 62 is in the form of a toggle switch, but it is contemplatedthat it could be a push-button switch, knob, lever or other user controlimplemented into the display cluster 64 or gauges. The mode switch 62has positions corresponding to an economy mode (ECO), a standard mode(STD) and a sport mode (SPORT), as will be described below in furtherdetail. The mode switch 62 can be toggled sequentially through thepositions corresponding to the economy mode, the standard mode, and thesport mode. The driver of the snowmobile 10 indicates a desire to changethe mode of operation from a current mode of operation CM to a desiredmode of operation DM for the snowmobile 10 by actuating the mode switch62 to the position corresponding to the desired mode DM. It iscontemplated that the modes of operation of the vehicle could be relatedto an authorization or identification of the driver, for example, asencoded in a key used to the start the vehicle 10. For example,different keys could be associated with different modes, or each keycould be authorized to operate the vehicle in one or more modes. It iscontemplated that the number and names of operation modes could bedifferent than as described herein.

The engine 24 is an internal combustion engine. The internalconstruction of the engine 24 may be of any known type and can operateon the two-stroke or four-stroke principle. The engine 24 drives acrankshaft 57 (FIG. 4A) that rotates about a horizontally disposed axis85 (FIG. 4A) that extends generally transversely to the longitudinalaxis 61 of the snowmobile 10. The crankshaft 57 drives the CVT 40, asdescribed in greater detail below, for transmitting torque to theendless drive track 65 for propulsion of the snowmobile 10.

FIG. 2A illustrates schematically a powertrain 75 of the snowmobile 10.The powertrain 75 includes the engine 24, the CVT 40 and a fixed-ratioreduction drive 78. The CVT 40 includes a driving pulley 80 coupleddirectly to rotate with the crankshaft 57 of the engine 24 and a drivenpulley 88 coupled to one end of a transversely mounted jackshaft 92which is supported on the frame 16 by bearings. As illustrated, thetransversely mounted jackshaft 92 traverses the width of the engine 24.The opposite end of the transversely mounted jackshaft 92 is connectedto the input member of the reduction drive 78 and the output member ofthe reduction drive 78 is connected to a drive axle 90 carrying sprocketwheels (not shown) that form a driving connection with the drive track65. Typically, the input member of the reduction drive 78 consists of asmall sprocket connected to the transverse jackshaft 92 and coupled todrive an output member consisting of a larger sprocket connected to thedrive axle 90 through a driving chain, all enclosed within the housingof the reduction drive 78.

In this particular example, the driving pulley 80 rotates at the samespeed ES as the crankshaft 57 of the engine 24 whereas the speed ofrotation of the transverse jackshaft 92 is determined in accordance withthe instantaneous ratio of the CVT 40. The drive axle 90 rotates at alower speed than the transverse jackshaft 92 because of the action ofthe reduction drive 78. It is contemplated that the driving pulley 80could be coupled to an engine shaft other than the crankshaft 57, suchas an output shaft, a counterbalance shaft, or a power take-off shaftdriven by and extending from the engine 24. Similarly, it iscontemplated that the driven pulley 88 could be coupled to a shaft otherthan the transverse jackshaft 92, such as directly to the drive axle 90or any other shaft operatively connected to the ground engaging elementof the vehicle (i.e. the drive track 65 in the case of the snowmobile10).

The driving pulley 80 of the CVT 40 includes a pair of opposedfrusto-conical sheaves, 82 and 84, between which the endless belt member86 is held. The driving pulley 80 will be described in greater detailbelow. The driven pulley 88 includes a pair of frusto-conical sheaves,87 and 89, holding the endless belt member 86 between them.

The gear ratio of the CVT 40 is defined as the ratio of the effectivediameter D2 of the driven pulley 88 to the effective diameter D1 of thedriving pulley 80. The effective diameters D1, D2 of the pulleys 80, 88are determined by the radial position of the belt 86 held between thetwo sheaves, 82 and 84, 87 and 89, of the respective pulleys 80, 88. Theradial position of the belt 86 held between two sheaves, 82 and 84, 87and 89, changes with the separation between the sheaves, 82 and 84, 87and 89. Since the length of the belt 86 remains constant, there is aninverse relationship between the effective diameters D1, D2 of thedriving and driven pulleys 80, 88. When the belt 86 moves radiallyoutwards on the driving pulley 80 (i.e. when the driving pulley sheaves,82 and 84, move towards each other), thereby increasing the effectivediameter D1 of the driving pulley 80, the belt 86 has to move radiallyinwards on the driven pulley 88 (i.e. the driven pulley sheaves, 87 and89, are moved away from each other), thereby decreasing effectivediameter D2 of the driven pulley 88, and changing the CVT gear ratio.

The driving pulley sheaves 82, 84 are biased away from each other sothat when not rotating, the driving pulley sheaves 82, 84 are far apartand the belt 86 is disengaged from the driving pulley 80. The moveablesheave moves in response to changes in engine speed ES. The effectivediameters D1, D2 of the pulleys 80, 88 are in inverse relationship. Asthe crankshaft 57 and the driving pulley sheaves 82, 84 begin to rotatewith increasing rotational speeds ES, the separation between the drivingpulley sheaves 82, 84 decreases due to the action of a set ofcentrifugal weights pushing the moveable sheave towards the fixedsheave. At a certain engine speed ES, the driving pulley sheaves 82, 84engage the belt 86 which in turn begins to rotate the driven pulleysheaves 87, 89. The rotational speed ES (of the crankshaft 57 anddriving pulley sheaves 82, 84) at which the driving pulley sheaves 82,84 engage the belt 86 is referred to as the engagement speedES_(engage).

For rotational speeds ES greater than the engagement speed ES_(engage),the engine 24 is operatively connected via the CVT 40 to the track 65.For rotational speeds ES less than the engagement speed ES_(engage), theCVT 40 is not engaged and thus the powertrain 75 cannot deliver torqueand power from the engine 24 to the track 65. The snowmobile 10 is thusnot being driven by the engine 24, and the engine 24 is in idleoperation for engine speeds ES less than the engagement speedES_(engage). Idle operation of the engine 24 enables powering of vehiclesystems such as the displays 64, the ECU 200, and the like. The engine24 can be placed in idle operation by releasing the throttle lever 37without turning off the engine 24. The engine 24 is typically turned onand off by inserting a key (mechanical and/or electronic) into a keyreceiver or by the operation of an on/off switch.

The engine 24 transmits torque via the crankshaft 57 to the drivingpulley 80 to rotate the driving pulley 80. The separation between thedriving pulley sheaves, 82 and 84, and the effective diameter of thedriving pulley 80 is controlled by an adjusting mechanism that will bedescribed in greater detail below. The belt 86 is engaged by the sheaves82, 84 of the driving pulley 80 as described above. The belt 86, inturn, engages the driven pulley 88, rotating the sheaves, 87 and 89,changing the separation therebetween, and the effective diameter D2 ofthe driven pulley 88 as described above. Torque is thus transferred fromthe engine 24 to the driving pulley 80, the belt 86, the driven pulley88 and finally to the drive axle 90.

When the CVT gear ratio is large (low gear), the driving pulley 80rotates several times for each rotation of the driven pulley 88. Thisconfiguration is desirable in certain situations such as, for example,during acceleration of the snowmobile 10, where it is necessary totransfer a large torque to the driving pulley 88, and thereby to thedrive axle 90.

When the CVT gear ratio is small (high gear), each rotation of thedriving pulley 80 results in multiple rotations of the driven pulley 88.This is useful in certain situations, such as, for example, when thesnowmobile 10 is being driven at constant and high speeds.

The engine 24 is an inline, two-cylinder, four-stroke, internalcombustion engine. It is however contemplated that the construction ofthe engine 24 may be of any known type. The engine 24 receives fuel fromthe fuel tank 25 via a fuel injection system 76 (FIG. 3). The engine 24receives air from an air intake system 66 (FIG. 2B) via a throttle body68. The fuel-air mixture in the engine 24 is ignited by an ignitionsystem 74. Engine output power P, torque τ and engine speed ES aredetermined in part by the fuel-air mixture in the engine 24 and theignition timing IT. The engine 24 is fluidly connected to a coolingsystem 284 for cooling the engine 24 during its operation. An enginecontrol unit (ECU) 200 is operatively connected to the engine 24 tocontrol operation of the engine 24 as will be discussed below.

With reference to FIG. 2B, the throttle body 68 comprises a throttlevalve 70 that regulates the amount of air flowing through the throttlebody 68 into the engine 24. The throttle valve 70 is a butterfly valvecomprising a circular disc mounted inside the tubular throttle body 68that rotates about a rod passing through a diameter of the disc. Thepassage of air through the tubular throttle body 68 is obstructed byvarying amounts as the disc rotates about the rod. The throttle valve 70is in a fully open position (minimal obstruction of air flow) when thecircular surface of the disc is at its minimum angle with respect to thecentral axis of the tubular throttle body 68, and in a fully closedposition (maximal obstruction of air flow) when the circular surface ofthe disc is at its maximum angle with respect to the central axis of thetubular throttle body 68. A throttle valve actuator 72, in the form ofan electric motor, is operatively connected to the throttle plate tochange the position of the throttle plate and thereby adjust the openingof the throttle valve 70. A throttle valve position TVP can be definedin terms of a degree of opening of the throttle valve 70. The throttlevalve position TVP is defined as a fraction of its fully open positionand thus varies from 0% (fully closed) to 100% (fully open). A throttlevalve sensor 206 is connected to the throttle valve 70 to sense thethrottle valve position TVP. The throttle valve actuator 72 positionsthe throttle valve 70 based at least in part on a position PP of thethrottle lever 37 of the snowmobile 10. As mentioned above, thesnowmobile 10 has a drive-by-wire (DBW) system in which the throttlevalve 70 is controlled electronically instead of having a mechanicallinkage between the throttle lever 37 and the throttle valve 70. Theposition PP of the throttle lever 37 is monitored by a throttle operatorposition sensor 204. The actuator 72 is controlled based in part onsignals received from the ECU 200, as described below.

With reference to FIGS. 2B and 3, the ECU 200 is in electroniccommunication with various sensors from which it receives signals. TheECU 200 uses these signals to control the operation of the throttlevalve actuator 72, the ignition system 74, and the fuel injection system76 in the case of a fuel injected engine, in order to control the engine24. The methods by which the ECU 200 controls the engine 24 will bedescribed in more detail below.

As it would be understood by those skilled in the art, not every sensoror component illustrated in FIG. 3 is required to achieve aspects of thepresent technology. As would also be understood by those skilled in theart, depending on the particular aspect of the technology, some of thesensors and components could be omitted, some of the sensors andcomponents could be substituted by other types of sensors andcomponents, and two or more sensors could be combined in a single sensorthat can be used to perform multiple functions without departing fromthe scope of the present technology.

The throttle operator position sensor 204 senses a position PP of thethrottle operator 37 (finger or thumb actuated throttle lever 37 in theillustrated implementation of the snowmobile 10) and sends a signalrepresentative of the throttle operator position PP to the ECU 200.Depending on the type of throttle operator, the throttle operatorposition sensor 204 is generally disposed in proximity to the throttleoperator 37 and senses the movement of the throttle operator 37 or thelinear displacement of a cable connected to the throttle operator 37.

The ECU 200 sends a signal to the throttle valve actuator 72 to adjustthe position TVP, and thereby the opening, of the throttle valve 70inside the throttle body 68. The throttle valve position TVP is adjustedbased in part on the throttle operator position PP as well as on otherfactors such as the ignition timing IT, required output power P andtorque τ, the current mode of operation CM, and the like.

The throttle valve position sensor 206 senses the position (i.e. thedegree of opening) of the throttle valve 70 and sends a signalrepresentative of the position TVP of the throttle valve 70 to the ECU200. The throttle valve position sensor 206 acts as a feedback to theECU 200 since the ECU 200 uses the signal received from the throttlevalve position sensor 206 to determine if the throttle valve actuator214 has moved the throttle valve 37 to the desired position and can makeadjustments accordingly. The throttle valve position sensor 206 can beany suitable type of sensor such as a rheostat, hall-effect sensor,potentiometer, and the like. Depending on the type of throttle valveactuator 72 being used, a separate throttle valve position sensor 206may not be necessary. For example, a separate throttle valve positionsensor 206 would not be required if the throttle valve actuator 72 is aservo motor since servo motors integrate their own feedback circuit thatcorrects the position of the motor and thus have an integrated throttlevalve position sensor 206.

An engine speed sensor 208 senses a speed of rotation ES of the engine24 and sends a signal representative of the speed of rotation ES of theengine 24 to the ECU 200. The engine speed sensor 208 is a hall-effecttype sensor coupled to a trigger wheel on the engine output shaft. It iscontemplated that the engine speed sensor 202 could be coupled to anyrotating shaft of the engine 24, such as the crankshaft. The rotationspeed ES of the engine 24 can be used by the ECU 200 to calculate theengine torque τ and the power output P of the engine 24.

A mode switch sensor 210 senses a position or a movement of the modeswitch 62 and sends a signal to the ECU 200 indicative of the desiredmode of operation DM (also referred to herein as the selected mode ofoperation of the vehicle). In some implementations, the mode switchsensor 210 is configured to sense a position of the mode switch 62 andthe ECU 200 determines the corresponding desired mode of operation DMfrom the signal received from the mode switch sensor 210. In someimplementations, the mode switch sensor 210 is configured to sense amovement of the mode switch 62, including the number of steps moved (oneor two steps in the illustrated implementation) and a direction ofmovement (“up” or “down”). The mode switch sensor 210 sends a signal tothe ECU 200 indicative of the movement and the ECU 200 determines thedesired mode of operation DM based on the current mode of operation CMand the information received about the movement of the mode switch 62.

A vehicle speed sensor 202 senses the speed VS of the snowmobile 10 andsends a signal representative of the speed VS of the snowmobile 10 tothe cluster 64. It is contemplated that the vehicle speed sensor 202could also send a signal representative of the speed VS of thesnowmobile 10 to the ECU 200. The vehicle speed sensor 202 is ahall-effect sensor coupled to a trigger wheel on a driveshaft, such asthe drive axle 90 so as to sense a rotational speed thereof. It iscontemplated that the vehicle speed sensor 202 could sense a speed ofany shaft driven by the driven pulley 88 (i.e. any shaft connectedbetween the driven pulley 88 and the track 65), including shafts insidethe reduction drive 78, to determine the speed of the snowmobile 10. Itis contemplated that any suitable type of vehicle speed sensor 202 couldbe used. Alternatively, the vehicle speed sensor 202 could include aglobal positioning system (GPS unit). By using information from the GPSunit, the speed of the vehicle 10 can be determined by calculating achange in position of the vehicle 10 over a period of time which isnormally a function of the GPS unit.

A driven pulley speed sensor 203 senses the speed N₂ of the drivenpulley 88 and sends a signal representative of the speed N₂ to the ECU200. The driven pulley speed sensor 203 is a hall-effect sensor coupledto the jackshaft 92 so as to sense a rotational speed thereof.

An altitude sensor 205 provided on the vehicle 10 determine the altitudeat which the vehicle 10 is operating and sends a signal to the ECU. Thealtitude sensor in the illustrated implementation is an air pressuresensor (or barometer) that detects the atmospheric pressure in thevicinity of the vehicle 10 and determines the altitude based on thedetected atmospheric pressure. It is contemplated that the sensor 205 isan altimeter. It is contemplated that the altitude sensor 205 could bepart of the GPS unit mentioned above.

An inclination sensor 280 is provided on the vehicle 10 to sense aninclination of the ground that the vehicle is operating on. It iscontemplated that the inclination sensor 280 could be part of the GPSunit mentioned above.

The ECU 200 is connected to the ignition system 74 to control ignitionof the fuel-air mixture in the combustion chamber of the engine 24. Forexample, the ECU 200 controls the ignition timing IT based partly on thethrottle valve position TVP, the throttle operator position PP, and/orengine speed ES. The ECU 200 is also connected to the fuel injectionsystem 76 to control fuel injection into the engine 24. The ECU isconnected to an engine coolant temperature sensor 288 for monitoring theengine coolant temperature flowing through the engine cooling system284, and thereby monitoring the operating temperature T_(E) of theengine 24.

The ECU 200 is connected to the display cluster 64 to control display ofinformation thereon. The ECU 200 sends signals to the display cluster 64to display information regarding engine and vehicle speed, and modeselection.

It is contemplated that the ECU 200 could be separated into multipleunits each having one or more of the functions described above andfurther below.

The ECU 200 controls operation of the engine 24 based at least in parton the signals received from the sensors 202, 203, 204, 205, 206, 208,210 and depending on the specific control scheme or map being used bythe ECU 200. The control maps provide information related to variousparameters (such as throttle valve position TVP, throttle operatorposition PP, fuel injection, ignition timing IT, engine torque, poweroutput, etc.) needed for operation of the engine 24. For example, acontrol map could provide information regarding the variation ofthrottle valve position and engine speed for achieving a particularpower output or engine torque. The ECU 200 may also use algorithms, inaddition to the control maps, to determine some of the parameters.

The snowmobile 10 can be operated in different modes of operation(sport, standard and economy in the illustrated implementation) asmentioned above. Some of the control maps used by the ECU 200 arespecific to each mode of operation and specify the variation of engineparameters for operation in that mode.

With reference to FIG. 2C, it can be seen that the throttle response(i.e. the throttle valve position TVP as a function of throttle operatorposition PP) is different for different modes. As mentioned above, thethrottle valve position TVP is defined as a fraction of its fully openposition and thus varies from 0% (fully closed) to 100% (fully open).The throttle operator position PP is also defined as a fraction of itsfully activated position and thus varies between 0% (unactivated oridle) and 100% (fully activated).

As the throttle operator position PP increases from 0% to 100%, thecorresponding throttle valve position TVP for each mode increases from aminimum value for that mode to a maximum value for that mode. Theminimum throttle valve position TVP corresponding to the 0% throttleoperator position PP is greater than zero for all three modes. It iscontemplated that the throttle valve position TVP corresponding to the0% throttle operator position PP could be zero for all three modes. Theminimum throttle valve position TVP corresponds to the idle throttlevalve position ITVP for that mode and is set at a value greater thanzero to enable idle operation in that mode.

As can be seen, for any given throttle operator position PP, thecorresponding economy mode throttle valve position TVP is lower than thecorresponding sport and standard mode throttle valve positions TVP.Furthermore, for any given throttle operator position PP other than100%, the sport mode throttle valve position TVP is greater than thecorresponding standard mode throttle valve position TVP. At the 100%throttle operator position PP the sport and standard mode throttle valvepositions TVP are equal.

In the illustrated implementation, the maximum throttle valve positionTVP in the sport and standard modes is set to be at its fully openposition (i.e. at 100%), while in the economy mode, the maximum throttlevalve position TVP is limited to 50% of its fully open position. It iscontemplated that the maximum throttle valve position TVP of thestandard mode could be less than that of the sport mode such that eachof the three modes has a different maximum throttle valve position TVP.It is also contemplated that the maximum throttle valve position TVP ofthe standard mode could be the same as that of the economy mode. In theillustrated implementation, for each of the three modes, the maximumthrottle valve position TVP is obtained when the throttle pedal 37 ispositioned at its maximum throttle position PP of a 100%. It iscontemplated that the maximum throttle valve position TVP could beobtained for a throttle operator position which is less than 100%.

The engine 24 of the snowmobile 10 is capable of delivering a certainmaximum output power based on its capacity as will be understood by aworker skilled in the art. The power P delivered by the engine 24 at anygiven instant is a function of, amongst other parameters, the throttlevalve position TVP, the ignition timing IT and the fuel injection. TheECU 200 controls operation of the engine 24 such that the output power Pdelivered by the engine 24 also depends on the current mode of operationCM. For example, in the economy mode, the output power P delivered bythe engine 24 is limited to a maximum value that is approximately 50% ofthe maximum output power available from the engine 24.

It is also contemplated that the vehicle speed could be limited in oneof the modes, for example, the vehicle speed could be limited in theeconomy mode, to increase fuel efficiency.

Turning now to FIGS. 4A and 4B, the driving pulley 80 will be describedin more detail.

As discussed above, the driving pulley 80 includes a pair of sheaves 82and 84, both of which rotate together with the crankshaft 57 about arotation axis 85 of the driving pulley 80. The term “axial direction”,as used herein in relation to the driving pulley 80, refers to adirection parallel to the rotation axis 85.

The inner and outer sheaves 82, 84 each have a belt-engaging surface 83.The belt 86 is held between the belt-engaging surface 83 of the drivingsheaves 82, 84. The inner sheave 82, disposed between the outer sheave84 and the engine 24, is fixed in the axial direction, and is thereforereferred to as the fixed sheave 82. The outer sheave 84 can move towardor away from the fixed sheave 82 in the axial direction in order tochange the drive ratio of the CVT 40, and is therefore referred to asthe movable sheave 84. It is contemplated that both sheaves 82, 84 couldbe moveable in the axial direction.

The sheaves 82, 84 of the driving pulley 80 are mounted on a drivingshaft 100 which is rotationally coupled to the crankshaft 57. A portion101 of the driving shaft 100 is taper-fitted on the end of thecrankshaft 57. A bolt 102 is inserted into the driving shaft 100 from anend opposite the portion 101 and screwed into the end of the crankshaft57 to retain the driving shaft 100 on the crankshaft 57. It iscontemplated that the driving shaft 100 could be rotationally coupled tothe crankshaft 57 in other known manners. For example, the driving shaft100 could engage the crankshaft 57 via splines.

The fixed sheave 82 is press-fit on the inner end of the driving shaft100 so as to be axially fixed and to rotate therewith.

The moveable sheave 84 is mounted on the driving shaft 100 axiallyoutwards of the fixed sheave 82. The moveable sheave 84 is mounted onthe driving shaft 100 on bearing sleeves 104 so as to be slidable in theaxial direction.

An annular spring chamber 110, coaxial with the driving shaft 100, isdefined between the moveable sheave 84 and the driving shaft 100. Ahelical compression spring 116 is disposed inside the spring chamber110, coaxial with the driving shaft 100. A flange 112 extending radiallyoutwards from the outer surface of the driving shaft 100 into the springchamber 110 forms a spring stop. The spring 116 is held in the springchamber 110 between the axially fixed spring stop 112 and an axiallymoveable outer wall 114 formed by a portion of the moveable sheave 84.This arrangement of the spring 116 biases the movable sheave 84 awayfrom the fixed sheave 82.

It is contemplated that the spring 116 could be held between a portionof the fixed sheave 82 and a portion of the moveable sheave 84, or anelement fixedly connected to the slidably moveable sheave 84. It is alsocontemplated that the spring 116 could be held between a portion of themoveable sheave 84 and an axially fixed portion of the driving pulley80, other than the flange 112, as long as the axially fixed portion isdisposed axially inward of the portion of moveable sheave 84.

A number of centrifugal weights 120 are mounted on the outer surface ofthe moveable sheave 84. In the illustrated implementation, thecentrifugal weights are in the form of flyweights or levers 120 havingone end 121 attached to the outer surface of the moveable sheave 84, andthe other end 122 being free to pivot away from the moveable sheave 84.When the moveable sheave 84 is at rest, the free end 122 of thecentrifugal levers 120 rests against its outer surface. As therotational speed of the moveable sheave 84 increases, the free end 122pivots away from the moveable sheave 84 and radially outwards withrespect to the driving shaft 100.

A spider 90 and coverplate 92 are mounted on the driving shaft 100,axially outward of the moveable sheave 84, so as to rotate with thedriving shaft 100. The coverplate 92 is fixed to the driving shaft 100by the bolt 102 that retains the driving shaft 100 to the crankshaft 57.The spider 90 is fixed to the coverplate 92 by bolts inserted into holes126 near its outer periphery. The spider 90 and the coverplate 92 thusrotate with the driving shaft 100.

The spider 90 has a cylindrical hub 124 that extends coaxially aroundthe driving shaft 100, and is spaced therefrom. The spider 90 has sixpairs of flanges 128 extending inwards towards the moveable sheave 84.The six pairs of flanges 128 are radially distributed along the outerperiphery. Each pair of flanges 128 has a roller 130 mounted rotatablybetween the ends thereof. Each roller 130 is in contact with acorresponding one of the centrifugal levers 120 of the moveable sheave84. The flange pairs 128 also engage complementary flanges 129 of themoveable sheave 84 so that the moveable sheave 84 rotates with thespider 90, and therefore with the driving shaft 100, about the axis 85.Each complementary flange 129 of the moveable sheave 84 is received inthe space between adjacent flange pairs 128 of the spider 90.

The spider 90 is made of aluminum. It is contemplated that the spider 90could be made of other suitable materials. The spider 90 has a pluralityof apertures 140 formed radially outwards of the hub 124 and between theflange pairs 128. The apertures 140 serve to reduce weight. It iscontemplated that the apertures 140 could be omitted.

The coverplate 92 is made of aluminum. It is contemplated that thecoverplate 92 could be made of other suitable materials. A plurality ofcavities 138 are formed in the surface of the coverplate 92 facing awayfrom the moveable sheave 84. The cavities 138 are formed for the purposeof the weight reduction. It is contemplated that the cavities 138 couldbe omitted.

At low engine operational speeds (RPM), the fixed sheave 82 and themoveable sheave 84 of the driving pulley 80 are positioned asillustrated in FIG. 4A. At high engine RPMs, the sheaves 82, 84 arepositioned as shown in FIG. 4B. The centrifugal weights 120, which helpto make this change in configuration, form part of the adjustmentmechanism for adjusting the CVT gear ratio.

With reference to FIG. 4A, when the driving shaft 100, and thus themoveable sheave 84 and spider 90 are at rest, the moveable sheave 84 isat its outermost position on the driving shaft 100 and at maximumseparation with respect to the fixed sheave 82. In this configuration,the rollers 130 of the spider 90 are in contact with the levers 120 nearthe end 121 attached to the moveable sheave 184.

As the moveable sheave 84 rotates faster, the free end 122 of the levers120 extend outwards pushing against the rollers 130, and pushing themoveable sheave 84 away from the spider 90 towards the fixed sheave 82.The point of contact of the lever 120 with the roller 130 moves from theend 121 attached to the moveable sheave 84 towards the free end 122 ofthe lever 120.

With reference to FIG. 4B, when the moveable sheave 84 is at itsinnermost position on the driving shaft 100, and at its closest positionto the fixed sheave 82, the free ends 122 of the levers 120 are incontact with the rollers 130 of the spider 90. This configuration of thedriving pulley 80 is achieved at high rotational speeds of the drivingshaft 100.

It is contemplated that the centrifugal weights 120 could be attached tothe spider 90 so as to be in contact with the moveable sheave 90, and topush the moveable sheave 84 away from the spider 90 with increasingrotational speed of the spider 90. It is also contemplated that thecentrifugal weights could be in the form of roller weights that rollradially outwards with increasing rotational speed of the driving pulley80. In such an implementation, surfaces in contact with the rollerweights are sloped such that the roller weights can push the moveablesheave away from the spider 90.

When the moveable sheave 84 is pushed towards the fixed sheave 82, thecompressed spring 116 exerts a force on the moveable sheave 84 to biasit away from the fixed sheave 82, i.e. in a direction opposite to theforce exerted on the moveable sheave 84 due to the centrifugal weights120. The balancing of these opposing forces, partly determines the axialposition of the moveable sheave 84. Thus, the centrifugal weights 120form the mechanical part of the adjustment mechanism for the CVT gearratio.

A piston 94, is slidably mounted on the driving shaft 100, axiallyinwards of the coverplate 92, and inside the cylindrical hub 124 of thespider 90. The piston 94 is sealed against the outer surface of thedriving shaft 100 by a seal 131 received in a groove formed in the innercylindrical surface of the piston 94. The piston 94 is sealed againstthe inner surface of the cylindrical hub 124 by a seal 133 received in agroove formed in the outer cylindrical surface of the piston 94. Thecylindrical hub 124 thus forms a cylinder for the piston 94. Forsimplicity, the cylindrical hub 124 will be referred to hereinafter asthe cylinder 124. The piston 94 is moved away from the coverplate 92 byfilling the space between the piston 94 and the coverplate 92 withpressurized air as will be described below.

In this implementation, the stationary moveable sheave 84 (i.e. moveablesheave 84 in its outermost axial position) abuts the piston 94 when itis not actuated, as shown in the configuration of FIG. 4A. It iscontemplated that the stationary moveable sheave 84 could be spaced fromthe piston 94 in its unactuated configuration. It is also contemplatedthat the piston 94 could be attached to the moveable sheave 84, so as toslide and rotate with the moveable sheave 84. It is contemplated thatthe piston 94 could be disposed in a cylinder that does not form part ofthe spider 90. It is also contemplated that the piston 94 could have adifferent shape than as shown herein. It is contemplated that aplurality of pistons, with a corresponding number of cylinders, could beprovided to apply force on the moveable sheave 84.

A connector 96 mounted on the coverplate 92 connects an air conduit 98to the interior of the cylinder 124 via air passages 93 formed in thecoverplate 92. The connector 96 rotates with the coverplate 92 while theair conduit 98 is stationary. Bearings 137 are inserted between thestationary air conduit 98 and the connector 96. The connector 96 isrotatably sealed against the stationary air conduit 98 via lip seals132. When pressurized air is fed through the air conduit 98 to thecylinder 124, the piston 94 slides away from the coverplate 92 pushingthe moveable sheave 84 towards the fixed sheave 82 and increasing theeffective diameter of the driving pulley 80. Thus, the force exerted onthe moveable sheave 84 by the piston 94 is in the same direction as thatexerted on the moveable sheave 84 due to the centrifugal weightmechanism.

As explained above, in general, a higher engine RPM causes fasterrotation of the driving pulley 80, increasing the force exerted on themoveable sheave 84 due to the centrifugal weights 120, resulting in alarger effective diameter for the driving pulley 80 (i.e. a smallereffective diameter for the driven pulley 88) and a lower gear ratio forthe CVT 40. Thus, the gear ratio of the CVT is determined by theoperation speed of the engine 24.

The pneumatically actuated piston 94 modifies the response curve of thedriving pulley 80. The driving pulley 80 achieves a larger effectivediameter for a given engine RPM when the centrifugal weight mechanism isassisted by the pneumatically actuated piston 94 than when the pneumaticpiston 94 is not actuated. The pneumatically actuated piston 94effectively shifts the snowmobile 10 into a higher gear with a smallerengine RPM than would be possible with a CVT 40 controlled solely bymechanical means (i.e. centrifugal weights 120). When the pressure isreleased so that the piston 94 is no longer actuated, the spring 116returns the moveable sheave 84 to its initial position so that the CVT40 returns to its purely mechanical characteristics with the effectivediameter of the driving pulley 80, and thus the CVT gear ratio, beingdetermined solely by the centrifugal weights 120.

Thus, the CVT 40 is fully operational with and without the pneumaticpiston 94 being actuated. The pneumatic piston 94 permits the CVT gearratio to be controlled independently of the engine RPM. For example, theCVT gear ratio can be adjusted based on consideration of factors suchas, torque required by the drive axle 90, fuel consumption, drivercomfort, or the like. The pneumatic pressure actuating the piston 94 canalso be adjusted to achieve the response curve desired. For example, theCVT 40 can be configured to maximize fuel economy, or performance, or tooptimize both. The pneumatically actuated piston 94 can also be used tosimulate the response of a multi-gear transmission. Several methods ofpneumatically controlling the CVT 40 will be described below in furtherdetail.

An electrical compressor 320 (FIG. 5) disposed elsewhere on thesnowmobile 10 is used to provide pressurized air for actuating thepiston 94. The compressor 320 includes an air-water separator to helpprevent or minimize moisture inside the CVT 40. It is contemplated thata mechanical compressor could be used instead. It is contemplated thatthe compressor 320 could be any suitable compressor that is capable ofachieving the requisite air pressure for actuation of the piston 94. Itis also contemplated that the compressor 320 could be powered by anengine other than the engine 24, a motor or battery as appropriate.

The air pressure applied to the piston 94 and the resultant piston forcethat fully converges the moveable and fixed sheaves 82, 84 toward eachother is much smaller for the CVT 40 of the implementation illustratedin FIGS. 4A and 4B, than for a CVT in which the gear ratio is solelypneumatically controlled. The size of the pump or compressor 320required to produce this piston force is much smaller than one requiredfor a fully pneumatically-controlled CVT, resulting in energy and spacesavings for the snowmobile 10.

An accumulator 322 (FIG. 5), serving as a reservoir of compressed air,is installed between the pump 220 and the cylinder 124 in order toensure a short response time for actuation of the piston 94 under alloperating conditions, and to limit pressure fluctuations.

It is also contemplated that pressurized gas cartridges could be usedinstead of the compressor 320 and accumulator 322 to provide pressurizedair for actuation of the piston 94.

The actuation of the piston 94 is controlled automatically based onparameters such the vehicle speed, engine rotation speed (RPM), torquerequired, fuel reserve and the like. Different methods of controllingthe CVT 40 have been described below.

It is contemplated that the actuation of the piston 94 couldadditionally be controlled manually by the operator of the snowmobile10. For example, a switch, such as a button switch, could be provided toswitch the actuation on or off. Alternatively, a continuously adjustableknob could be provided to allow the driver of the snowmobile to set theamount of force being exerted by the piston 94.

With reference to FIG. 5, the pneumatic system 300 for deliveringpressurized air to the piston 94, and the pneumatic control unit (PCU)310 for automatically controlling pneumatic actuation of the piston 94will now be discussed in more detail.

The pneumatic system 300 includes a compressor 320, an electric motor340, an accumulator 322, a pressure regulation unit 328 including an airinlet valve 324, an air outlet valve 326, and a cylinder pressure sensor330, and an accumulator pressure sensor 332.

The PCU 310 regulates the pneumatic air pressure delivered to the piston94 for selective and adjustable actuation of the piston 94.

As discussed above, the cylinder 124 is connected to the compressor 320for receiving pressurized air. The compressor 320 is operativelyconnected to the PCU 310. The PCU 310 sends electronic signals to thecompressor 320 for activation thereof. It is contemplated that the PCU310 could also be configured to receive signals from the compressor 320.

As also discussed above, an accumulator 322, in fluid communication withthe compressor 320 (connected downstream of the compressor), storescompressed air for actuation of the piston 94 and helps to reduce theresponse time for actuation of the piston 94. Thus the compressor 320 isconnected to the cylinder 124 via the accumulator 322. Pressurized airflows from the compressor 320 to the accumulator 322, and from theaccumulator 322 to the cylinder 124. It is contemplated that anadditional air flow path could be provided for pressurized air to flowfrom the compressor 320 to the cylinder 124 without passing through theaccumulator 322. It is contemplated that the accumulator 322 could beomitted.

An air inlet valve 324, connected between the accumulator 322 and thecylinder 124 allows air flow from the accumulator 322 to the cylinder124. The air inlet valve 324 is opened when the pressure inside thecylinder 124 (as determined by the cylinder pressure sensor 330) is lessthan desired, and if pressurized air at a higher pressure than that inthe cylinder 124 is available from the accumulator 322 (as determined bythe accumulator pressure sensor 332).

An air outlet valve 326 connected to the cylinder 124 allows pressurizedair in the cylinder 124 to be vented to the atmosphere. The air outletvalve 326 is opened if the pressure in the cylinder 124 is greater thandesired.

The air inlet valve 324 and the air outlet valve 326 are eachoperatively connected to the PCU 310. The valves 324, 326 can each beconfigured to open at particular pressure set-points. The pressureset-points for the valves 324, 326 can be assigned electronically oradjusted mechanically. The PCU 310 sends control signals to the valves324, 326 to actuate their opening and closing. It is contemplated thatthe PCU 310 could also be configured to receive signals from the valves324, 326. It is contemplated that the air inlet valve 324 and the airoutlet valve 326 could be replaced with a single proportional relayvalve.

An accumulator pressure sensor 332 is connected to the accumulator 322to measure the air pressure in the accumulator 322. In the illustratedimplementation, the accumulator pressure sensor 332 is connecteddownstream of the accumulator 322, between the accumulator 322 and theair inlet valve 324. It is however contemplated that the accumulatorpressure sensor 332 could be connected elsewhere on the accumulator 322.

A cylinder air pressure sensor 330 measures the air pressure in thecylinder 124. The cylinder air pressure sensor 330 is shown connectedbetween the air inlet valve 324 and the cylinder 124.

The pressure sensors 330, 332 are each communicatively connected to thePCU 310. The PCU 310 is configured to receive data and/or signals fromthe pressure sensors 330, 332 indicative of the air pressure sensed bythe pressure sensors 330, 332. It is contemplated that the PCU 310 couldalso be configured to send control or data signals to the pressuresensors 330, 332. The PCU 310 is further configured to send controlsignals to the air inlet valve 324, the air outlet valve 326, and thecompressor 320 based in part on the signals received from the pressuresensors 330, 332.

As mentioned above, it is contemplated that a pressurized gas cartridgecould be used instead of the compressor 320 and accumulator 322. In suchan implementation, the PCU 310 would be operatively connected to the gascartridge, and configured to send control or data signals thereto basedon signals received from other sensors such as the cylinder pressuresensor 330.

The PCU 310 is in communication with the ECU 200 for controllingoperation of the piston 94. It is contemplated that some or all thefunctions of the PCU 310 could be integrated with the ECU 200.

In the illustrated implementation of the snowmobile 10, a piston forceselector 380 is also provided. The piston force selector 380 is operableby the driver of the snowmobile 10 for actuating the piston and?orselecting a desired piston force Pf. The PCU 310 communicates with thepiston force selector 380 for optionally controlling the piton force Pfbased in part on the selected piston force. The piston force selector380 could be in the form of a push-button, switch, knob, lever, or thelike, that can be moved between a plurality of piston force selectionpositions, for example, 0, low and high.

Turning now to FIGS. 6 to 10, several methods of pneumaticallycontrolling the CVT 40 will now be described.

In the illustrated implementation of the method of controlling the CVT40, the centrifugal weights 120 of the CVT 40 are optimized foroperating in the SPORT mode and at a high altitude (defined, in thisimplementation of the vehicle 10, as 2000 m above sea level and higher).Thus, in the SPORT mode and at a high altitude, the force Fp applied bythe piston 94 on the moveable sheave 84 is zero. The driving pulleydiameter D1 is determined based on the engine speed ES, which is in turncontrolled by the ECU 200 based on an engine speed control map (notshown) for the sport mode.

In the absence of any force Fp being applied by the piston 94, theengine speed ES obtained for a given throttle valve position TVP andignition timing IT is greater at low altitudes than at high altitudesdue to the increased atmospheric air pressure at low altitudes. Thehigher atmospheric air pressure at low altitudes results in a greateramount of air being inducted through the throttle body into thecombustion chamber for the same throttle valve opening TVP. In order tomaintain the stoichiometric ratio of the fuel-air mixture, a greateramount of fuel is injected to the engine 24 at low altitudes than athigh altitudes which therefore produces more power, and rotates thecrankshaft 57 at a higher engine speed ES for the same throttle valveopening TVP.

The pneumatic piston 94 allows the engine speed ES to be controlledindependently of the throttle valve position TVP. The pneumatic pistoncan be actuated to reduce the engine speed ES and thus compensate forthis altitude related increase in engine speed ES.

Turning now to FIG. 6, the method 400 of controlling the CVT 40 tocompensate for altitude will be described in detail.

The method starts at step 410 where the PCU 310 determines the altitudebased on the signal received from the altitude sensor.

Then, at step 420, the PCU 310 determines the operation mode based onthe signal received from the mode switch 62 or based on a key.

Then the method 400 proceeds to step 430, where it determines whetherthe mode is SPORT and the altitude is at least as great as a highaltitude threshold A_(HT) (i.e. the altitude is high), based on signalsreceived from the mode switch sensor 210 and the altitude sensor 205 viathe ECU 200. In the illustrated implementation, the high altitudethreshold A_(HT) is set to be 2000 m, but it is contemplated that thehigh altitude threshold A_(HT) could be other than 2000 m. If at step430, the mode is determined to be SPORT, and the altitude is determinedto be high, the method 400 proceeds to step 435 where the piston forceFp is set to be zero for all values of throttle operator position PP anddriven pulley speed N₂. If at step 430, the mode is determined to not beSPORT (i.e. mode is STD or ECO), or if the altitude is determined to be2000 m or less (i.e. the altitude is low), the method 400 proceeds tostep 440.

At step 440, the PCU 310 determines the throttle operator position PPbased on the signal received from the throttle position sensor 204 andthen proceeds to step 450, where the PCU 310 determines the drivenpulley speed N₂ based on the signal received from the driven pulleyspeed sensor 203. The method 400 then advances to step 460.

At step 460, the PCU 310 obtains the desired piston force Fp to beapplied to the piston 94 from the appropriate piston force control mapfor the given mode and altitude. If the mode is SPORT and the altitudeis low, the PCU 310 obtains piston force Fp from the SPORT MODE-LOWALTITUDE control map (FIG. 7). If the mode is STD and the altitude islow, the PCU 310 obtains piston force Fp from the STD MODE-LOW ALTITUDEcontrol map (FIG. 8B). If the mode is STD and the altitude is high, thePCU 310 obtains piston force Fp from the STD MODE-HIGH ALTITUDE controlmap (FIG. 8A). For ECO mode and low altitude, the PCU 310 obtains pistonforce Fp from the ECO MODE-LOW ALTITUDE control map (FIG. 9B), and forECO mode and high altitude, the PCU 310 obtains piston force Fp from theECO MODE-HIGH ALTITUDE control map (FIG. 9A).

Finally, at step 470, the PCU 310 adjusts the pneumatic pressure P inthe cylinder 144 based on the desired piston force Fp obtained from therelevant control map in step 470. The PCU 310 receives signals from thepressure sensors 330, 332 and sends signals to the compressor 340, andthe valves 324, 326 to adjust the pneumatic pressure to the desiredvalue.

In the illustrated control method 400, the PCU 310 uses the highaltitude control map for any altitude greater than or equal to the highaltitude threshold A_(HT), and the sea level control map for altitudesof lower than the high altitude threshold A_(HT). It is contemplatedthat, for intermediate altitudes between high altitude threshold A_(HT)and sea level, the PCU 310 could interpolate between the high altitudeand sea level control maps for the given mode. It is contemplated thatmore than two control maps could be used for altitude compensation, forexample, an additional control map could be provided for intermediatealtitudes between the high altitude threshold A_(HT) and sea level. Itis contemplated that a low altitude threshold A_(LT) could be defined, alow altitude control map could be used for altitudes up to the lowaltitude threshold A_(LT), and an intermediate altitude control mapcould be used for altitudes between the low altitude threshold A_(LT)and high altitude threshold A_(HT). It is contemplated that a controlmap could also be provided for altitudes below sea level.

When the vehicle 10 is operated at sea level in the SPORT mode, thepiston 94 applies a force Fp on the moveable sheave 84 of the drivingpulley 80 based on the throttle operator position PP and the drivenpulley speed N₂ (which is related to the vehicle speed VS in a knownmanner). It is contemplated that the piston force Pf could be determinedbased on the throttle valve position TVP instead of the throttleoperator position PP. FIG. 7 shows a piston force control map 700 forlow altitudes and in sport mode.

As can be seen in FIG. 7, a piston force Pf is exerted when the throttleoperator position PP is greater than a minimum threshold PP2 (about 20%in this implementation) or when the driven pulley speed N₂ exceeds athreshold N2 a (about 5000 rpm in this implementation). For any givendriven pulley speed N₂, the piston force Pf increases with increasingthrottle operator position PP up to a maximum (in the illustratedimplementation, the maximum piston force Pf is exerted at about 75%throttle operator position PP). Thereafter the piston force Pf decreaseswith increasing throttle operator position PP. A piston force Pf is notapplied when the driven pulley speed N₂ is zero unless the throttleoperator position PP exceeds a threshold PP1 (about 60% in theillustrated implementation). In the regime of high driven pulley speedN₂ and low throttle operator positions PP regime (PP<PP2, N2>N2 a), thePCU 310 applies a small but non-zero piston force Pf. For throttleoperator position PP greater than PP2, the piston force Fp generallyincreases with driven pulley speed N₂, up to a maximum piston force Fpand then decreases with increasing driven pulley speed N₂.

With reference to FIG. 8A, when operating in the STD mode at highaltitude, the piston 94 applies a force Fp on the driving pulley sheave84 so as to lower the gear ratio (D1/D2) and obtain a lower engine speedES for a given vehicle speed VS as compared to SPORT mode. The pistonforce Fp applied is non-zero only when the throttle operator position PPexceeds a given minimum (20% in the illustrated implementation) and whenthe driven pulley speed N₂ is below a maximum (8000 rpm in theillustrated implementation). The piston force Fp is highest forintermediate values of driven pulley speed (approximately 5000 rpm inthe illustrated implementation).

As can be seen from the control map 800′ shown in FIG. 8B, whenoperating in the STD mode at sea level, for any given combination ofdriven pulley speed N₂ and throttle operator position PP, the pistonforce Fp on the driving pulley sheave 84 is larger compared to thestandard mode piston force at high altitude, as well as the sport modesea level piston force

As can be seen from the control map 900 shown in FIG. 9A, when operatingin the ECO mode at high altitude, the piston 94 generally applies agreater force Fp on the driving pulley sheave 84 than in the standardmode at high altitude so as to further lower the gear ratio (D1/D2)compared to the standard mode at high altitude. The piston force Fp, inthe economy mode at high altitude is however not as high as the pistonforce Fp applied in the standard mode at sea level (FIG. 9B). In theeconomy mode at sea level, the piston force Fp is non-zero for allvalues of driven pulley speed N₂. At high altitude, the piston force Fpapplied is non-zero only when the throttle operator position PP exceedsa given minimum (20% in the illustrated implementation which is the sameas in the standard mode). The piston force Fp is highest forintermediate values of driven pulley speed (approximately 5000 rpm inthe illustrated implementation).

As can be seen from the control map 900′ shown in FIG. 9B, whenoperating in the economy mode at sea level, and as previously mentioned,the piston 94 force Fp on the driving pulley sheave 84 is increasedcompared to the economy mode high altitude piston force Fp as well asthe standard mode sea level piston force Fp. The piston force Fp isincreased in order to compensate for the increased engine speed ES dueto the increase in air pressure.

It is contemplated that the control maps 700, 800, 800′, 900, 900′discussed above for controlling the piston force Pf could correspond todifferent air pressures instead of different altitudes.

It is contemplated that, in addition to the control maps 700, 800, 800′,900, 900′ used in the altitude compensation method 400 of FIG. 6, thePCU 310 could also be connected to the ECU 200 and/or other sensors suchas the engine speed sensor 208, in a closed loop feedback control foradjusting the piston force Pf to achieve a target engine speed ES.

Turning now to FIG. 10, a parking or drive-away control function of thePCU 310 will be described in detail.

When the vehicle 10 is started, the engine 24 has to be revved up so asto increase the engine speed ES beyond the engagement speed ES_(engage)in order to engage the CVT 40. Typically, the driver presses on thethrottle lever 37 to increase the throttle operator position PP and tothereby increase the throttle valve opening TVP and increase the enginespeed ES. The revving up of the engine 24 in this manner typicallygenerates considerable noise in addition to increased fuel consumption.

With reference to FIG. 10, in the present implementation, the CVT 40 ispneumatically controlled using the control map 1000 in order to enable asmoother start-up of the vehicle 10 with reduced noise and fuelconsumption. The CVT 40 is also pneumatically controlled when thevehicle 10 is moving at a low vehicle speed VS and when the engine 24 isoperating at a low engine speed ES.

When a pneumatic force P is applied to the piston 94, the moveablesheave 84 is pushed towards the fixed sheave 82 to engage the belt 86,thereby lowering the engagement speed ES_(engage). By reducing theengagement engine speed ES_(engage), pneumatic control of the CVT 40enables a quieter start with reduced fuel consumption. Once the CVT 40is engaged, a further increase in the piston force Fp results in anincrease in driven pulley speed N₂ and vehicle speed VS. After startingthe engine 24, and engaging the CVT 40, if the driver continues toincrease the throttle operation position PP, the PCU 310 increases thepiston force Fp on the sheave 84 so that the vehicle speed VS canincrease without requiring as much of an increase in the engine speed ESas would be needed in the absence of the pneumatic system 300. Thisrelative reduction of engine speed ES also leads to less noise and fuelconsumption.

As can be seen in FIG. 10, the parking function piston force Pfincreases with the throttle operator position PP, with the rate ofincrease being higher for throttle operator positions PP below athreshold throttle operator position PP9 (10% in the illustratedimplementation). The threshold throttle operator position PP9 isgenerally set to be at the level where the vehicle 10 starts moving. Inthe region 1010 of the control map 1000, (PP<PP9), the vehicle 10 hasnot yet started moving while in the region 1020 (PP>PP9), the vehicle 10is moving at slow speeds VS and the engine 24 is operating at low enginespeeds ES). A parking function piston force Pf is applied for throttleoperator positions PP up to 50% and the maximum parking function pistonforce Pf applied is approximately 700N (in this implementation, where atotal force of about 2000N is needed to increase the driving pulleydiameter to its maximum value.

As can be seen in FIG. 10, the piston force Fp applied to the CVT 40 isalso dependent on the engine temperature T_(E). If the engine 24 isalready warm when the vehicle 10 is started, for example, if the engine24 is started up shortly after having been shut down, the piston forcePf applied is such that the engagement speed reduction is slightlygreater than if the engine 24 were started from cold. When the engine 24is cold, it is desirable to warm up the engine 24 by allowing it tooperate at slightly higher speeds. Therefore, the force applied by thepiston 94 is higher for higher engine temperatures T_(E). Thetemperature dependence of the piston force Pf is influenced by a numberof parameters, including those related to the pneumatic system, such asfriction, thermal expansion, and the like. It is also contemplated thata the piston force Pf applied could be lower at higher temperatures.

The piston force Pf is also based on the mode of operation. In the sportmode, the CVT 40 is operated purely mechanically without applying anypiston force Pf in order to obtain a large torque and enable the vehicle10 to accelerate faster. A non-zero piston force Pf is applied in theSTD and ECO modes. In the illustrated implementation, for a given enginetemperature and throttle operator position PP, the piston force Pf isthe same in the STD and ECO modes. The control map 1000 shown in FIG. 10is used in both of the STD and ECO modes. It is however contemplatedthat different piston force control maps could be used in the STD andECO modes to apply different piston forces. For example, for a giventhrottle operator position PP, the piston force Pf could be greater inthe ECO mode than in the STD mode.

The PCU 310 causes application of a parking function piston force whenit determines a parking/drive-away condition that is indicative of thevehicle 10 being in the process of parking or driving away from a parkedposition. The PCU 310 determines a parking/drive-away condition if thevehicle speed VS is smaller than a parking start threshold vehicle speedVS_(P1), and the engine speed ES is lower than a parking thresholdengine speed ES_(P1). The parking threshold engine speed ES_(P1) is setto 1500 rpm in the illustrated implementation. In some implementations,the parking/drive-away conditions include the brake 38 not beingactuated.

When the parking/drive-away conditions above are satisfied or detected,and if the vehicle 10 is not in a SPORT mode of operation, the PCU 310accesses the parking control map of FIG. 10 to adjust the pneumaticpressure P in order to create the piston force Pf obtained from theparking piston force control map 1000. If the vehicle 10 is in a SPORTmode and if the pneumatic pressure is at a non-zero level, the PCU 310releases to the pneumatic pressure to ensure that the CVT is onlymechanically controlled. Typically, however, the pneumatic pressure Pand the piston force Pf are zero when the vehicle 10 is started. If aclosed loop feedback control is being used for adjusting of the pistonforce Pf, it is deactivated when the parking function piston force isapplied. It is contemplated that a piston force Pf could be applied evenif the vehicle 10 is operating in a SPORT mode and theparking/drive-away conditions are detected. Therefore, in someimplementations, a parking force control map could be provided for theSPORT mode as well.

In some implementations, the parking function piston force Pf is removedwhen the PCU 310 determines that the vehicle 10 has started moving(i.e., when the vehicle speed increases above a parking end thresholdvehicle speed, VS_(P2)). In the illustrated implementation, the parkingend threshold vehicle speed VS_(P2) is greater than the parking startthreshold vehicle speed VS_(P1). It is however contemplated that theparking start threshold vehicle speed VS_(P1) could be the same as theparking end threshold vehicle speed VS_(P2).

In the illustrated implementation, the vehicle 10 is considered to bemoving and the parking function piston force Pf is removed when vehiclespeed VS increases above the parking end threshold vehicle speed VS_(P2)(which is set to be at 10 km/h in the illustrated implementation), andwhen the engine speed ES is greater than a parking threshold enginespeed ES_(P2) (set to be at 2200 rpm for the ECO mode in the illustratedimplementation).

The parking threshold engine speed ES_(P2) is greater for the STD modethan for the ECO mode. The PCU 310 also stops application of the parkingfunction piston force Pf if the PCU 310 determines that the engine speedES is close to an engine stall speed ES_(stall) which is different fordifferent modes, and is generally lower than the idle engine speedES_(idle) for that mode. Additionally, if the brake 38 is determined tobe actuated, the PCU 310 stops application of the parking functionpiston force Pf.

Turning now to FIGS. 11A and 11B, a minimum force control of the CVT 40will be described in detail.

When a vehicle 10 is moving downhill, the driver sometimes releases thethrottle operator 37 or holds the throttle operator 37 at a low position(i.e. PP-0%) since the vehicle 10 is being accelerated due to gravity.The ECU 200 therefore decreases the throttle valve position TVP inaccordance with the throttle operator position PP. In ECO and STD mode,as a result of the throttle valve position TVP decreasing, the enginespeed ES could decrease to almost zero and could cause the belt 86 ofthe CVT to disengage from the driving pulley 82 while the vehicle 10continues to roll downhill. In order to prevent disengagement of the CVT40 in the ECO and STD modes, the PCU 310 controls the piston force Pf tobe at least as great as a minimum piston force Pfmin to keep the CVT 40engaged.

When the CVT 40 is engaged (due to the minimum piston force control ofthe CVT 40), the vehicle speed VS and therefore driven pulley speed N2is greater than the driving pulley speed N₁ and the engine speed ES. Thedriven pulley 88 drives the driving pulley 80 and the engine outputshaft 57. In this negative load condition, the rotational speed ES ofthe engine crankshaft 57 driven by the driven pulley 88 is greater thanthat would be achieved if the crankshaft 57 were being driven by theengine 24 based on the low throttle valve position TVP. As the vehicle10 continues to roll downhill and the driven pulley 88 drives thedriving pulley 80 and the engine output shaft 57, the rotational speedof the driven pulley 88, and thereby the vehicle speed VS decreases.This deceleration of the vehicle 10 is smoother compared to that whenthe brakes 38 are actuated.

With reference to FIGS. 11A and 11B, the minimum piston force Pfmin isdefined based on the engine speed ES, the engine temperature T_(E), andthe mode of operation as can be seen from the maps 1100 and 1100′ ofFIGS. 11A and 11B. The PCU 310 accesses the control map 1100 in the STDmode and the control map 1100′ in the ECO mode to obtain the pistonforce Pf to be applied to the driving pulley 80. In the SPORT mode, thePCU 310 sets the piston force Pf to be zero. Thus the CVT 40 iscontrolled purely mechanically in the SPORT mode. It is contemplatedthat a minimum piston force could also be defined for the SPORT mode.

In the illustrated implementation, the minimum piston force control ofthe CVT 40, as described above with reference to FIGS. 11A and 11B, isactivated when the PCU 310 determines that the engine speed ES is abovea threshold speed ES11. The PCU 310 stops applying the piston force Pffrom the downhill minimum force control map 1100, 1100′ if the enginespeed ES decreases below the threshold speed ES11, or if the driverswitches the operation mode from STD and ECO modes to the SPORT mode.

It is also contemplated that the minimum piston force control could beactivated when a negative load condition is detected, i.e. when theengine speed ES is greater than a downhill threshold engine speed and atleast one of the following is true: the throttle operation position PPis lower than a downhill threshold throttle operation position, and thethrottle valve position TVP is lower than a downhill threshold throttlevalve position.

The PCU 310 also controls the pneumatic piston 94 in order to preventstalling of the engine 24 as will be described below.

The engine 24 can stall, for example, if the throttle operator 37 issuddenly released and the brake 38 actuated, causing the throttle valveTVP to be closed by the ECU 200. Another example of a situation wherethe engine 24 could stall is when the brake 38 is actuated while theground engaging member of the vehicle 10, whether it be wheels or thetrack 65, is not in contact with ground. If the piston 94 is currentlyactuated when a situation that could cause the engine 24 to stalloccurs, the PCU 310 causes the pneumatic valve 326 to be opened, therebyventing the pressure P on the piston 94, and quickly deactuating thepiston 94. When the piston 94 is deactuated, the CVT 40 disengages,thereby isolating the engine 24 from the suddenly braking wheels. Theengine 24 would continue operating at low engine speeds less thanES_(engage), so that when the driver releases the brake 38 and beginsactuating the throttle operator 37, the engine speed ES can be quicklyincreased in response to the throttle operator position PP.

The stall protection control of the CVT 40 by the PCU 310 is activatedwhen the PCU 310 detects a stall condition. In the illustratedimplementation, the stall condition includes a high negative rate ofchange of the driven pulley speed N₂. In the illustrated implementation,the rate of change of the driven pulley speed is determined to be highwhen the magnitude of the rate of change is than greater than a stallthreshold rate, which is set to be 150 rpm/s². It is howevercontemplated that the stall threshold rate could be different than 150rpm/s². It is also contemplated that the stall protection control couldbe activated if the brake 38 is actuated when a high negative rate ofchange of the driven pulley speed N₂ occurs.

The pneumatic piston 94 is controlled by the PCU 310 to enable a smoothstart from a temporary stop on an uphill gradient. When the brake 38 isdeactuated after having been actuated, if the PCU 310 detects anopposite direction of rotation of the driven pulley 88 (negative drivenpulley speed N₂), the PCU 310 determines that the vehicle 10 ispositioned on an incline and facing uphill stand condition).Alternately, the detection of the uphill stand condition could also bebased in part on the inclination of the ground as determined by theacceleration sensor 205 or the inclination sensor 280 provided on thevehicle 10.

When the uphill stand condition is detected, the PCU 310 increases thepiston force Fp at a defined rate (˜2000N/s in the illustratedimplementation). The PCU 310 continues to increase the piston force Pfeither until the driven pulley speed N₂ is detected to be zero, or up toa pre-defined maximum piston force Fp (700N in the illustratedimplementation). In the illustrated implementation, the piston force Pfis increased at a rate such that the piston force Pf reaches the maximumpiston force within an uphill stand threshold time period. In theillustrated implementation, the uphill stand threshold time period is 1second.

If the driven pulley speed N₂ is detected to be zero, the piston forcePf is maintained at the level at which driven pulley speed N₂ isdetected to be zero. Once the piston force Pf increases to thepre-defined maximum level for the uphill stand condition control, thepiston force Pf is maintained at that level. The uphill stand pneumaticcontrol of the CVT 40 ends when the throttle operator 37 is actuated bythe driver, i.e. when throttle operator position PP is non-zero, PP>0 orwhen the brake 38 is actuated, at which point, the piston force Fp isreturned to its default value (i.e. the value based on its mode ofoperation, engine speed ES and other operational parameters).

The above description referred to a snowmobile 10 having a CVT 40 with apneumatic piston 94. It should however be understood that the controlmethods could be applied to other vehicles and devices which use a CVT.It will also be understood that the piston 94 could be actuatedhydraulically, with oil or other such incompressible fluids, instead ofpneumatically with compressed gas.

Modifications and improvements to the above-described implementations ofthe present technology may become apparent to those skilled in the art.The foregoing description is intended to be exemplary rather thanlimiting. The scope of the present technology is therefore intended tobe limited solely by the scope of the appended claims.

What is claimed is:
 1. A method of operating a vehicle at differentaltitudes, the vehicle comprising: an engine; a throttle operator beingoperable by a driver of the vehicle; a throttle valve regulating airflowto the engine, a throttle valve position of the throttle valve beingbased at least in part on a throttle operator position of the throttleoperator; a continuously variable transmission (CVT) operativelyconnected to the engine, the CVT including a driving pulley, a drivenpulley, and a belt operatively connecting the driving pulley to thedriven pulley; at least one ground engaging member operatively connectedto the driven pulley and comprising at least one of: a wheel and atrack; a piston operatively connected to the driving pulley for applyinga piston force to the driving pulley when actuated and thereby changingan effective diameter of the driving pulley; and a control unit forcontrolling actuation of the piston and the piston force, the methodcomprising: determining at least one of an altitude and an atmosphericpressure; determining a driven pulley speed; determining at least one ofthe throttle operator position and the throttle valve position;selectively actuating the piston based on the at least one of thealtitude and the atmospheric pressure; controlling the piston forcebased on: the driven pulley speed; and the at least one of: the throttleoperator position and the throttle valve position; and controlling thepiston force based on at least a first control map corresponding to afirst altitude and a second control map corresponding to a secondaltitude based on the determined at least one of the altitude and theatmospheric pressure.
 2. The method of claim 1, wherein: the one of thealtitude and the atmospheric pressure is the altitude; and the pistonforce is set to be zero responsive to the determined altitude beinggreater than a high altitude threshold.
 3. The method of claim 2,wherein the high altitude threshold is 2000 m.
 4. The method of claim 1,wherein the vehicle further comprises a mode switch for selecting one ofa plurality of modes of operation of the vehicle, the method furthercomprising: determining the one of the plurality of modes of operationthat has been selected; and controlling the piston force based at leastin part on the selected one of the plurality of modes of operation ofthe vehicle.
 5. The method of claim 4, wherein: the plurality of modesincludes a first mode and a second mode; each of the first control mapand the second control map is associated with the first mode; and thecontrolling of the piston force based at least in part on the selectedone of the plurality of modes of operation of the vehicle comprises:controlling the piston force based at least in part on the one of thefirst control map and the second control map when the selected one ofthe plurality of modes of operation of the vehicle is the first mode;and controlling the piston force based at least in part on a thirdcontrol map corresponding to the first altitude and associated with asecond mode when the selected one of the plurality of modes of operationof the vehicle is the second mode.
 6. The method of claim 1, wherein thepiston is at least one of pneumatically actuated and hydraulicallyactuated.
 7. The method of 2, wherein the piston is at least one ofpneumatically actuated and hydraulically actuated.
 8. The method of 3,wherein the piston is at least one of pneumatically actuated andhydraulically actuated.
 9. The method of 4, wherein the piston is atleast one of pneumatically actuated and hydraulically actuated.
 10. Themethod of 5, wherein the piston is at least one of pneumaticallyactuated and hydraulically actuated.
 11. A vehicle comprising: anengine; a throttle operator being operable by a driver of the vehicle; athrottle valve regulating airflow to the engine, a throttle valveposition of the throttle valve being based at least in part on athrottle operator position of the throttle operator; a continuouslyvariable transmission (CVT) operatively connected to the engine, the CVTincluding a driving pulley, a driven pulley, and a belt operativelyconnecting the driving pulley to the driven pulley; at least one groundengaging member operatively connected to the driven pulley andcomprising at least one of: a wheel and a track; a piston operativelyconnected to the driving pulley for applying a piston force to thedriving pulley when actuated and thereby changing an effective diameterof the driving pulley; and a control unit for controlling actuation ofthe piston and the piston force; and an altitude sensor sensing at leastone of an altitude and an atmospheric pressure, the control unit beingconfigured to control actuation of the piston and to control the pistonforce based on at least a first control map corresponding to a firstaltitude and a second control map corresponding to a second altitudebased on the sensed at least one of the altitude and the atmosphericpressure.
 12. The vehicle of claim 11, wherein the vehicle furthercomprises a mode switch for selecting one of a plurality of modes ofoperation of the vehicle, the control unit being further configured tocontrol the piston force based at least in part on the selected one ofthe plurality of modes of operation of the vehicle.
 13. The vehicle ofclaim 11, wherein the vehicle further comprises at least one of ahydraulic system and a pneumatic system connected to the piston, thecontrol unit being connected to the at least one of the hydraulic systemand the pneumatic system for controlling the piston force.
 14. Thevehicle of claim 12, wherein the vehicle further comprises at least oneof a hydraulic system and a pneumatic system connected to the piston,the control unit being connected to the at least one of the hydraulicsystem and the pneumatic system for controlling the piston force.